Correlation of microstructure and fracture properties of API X70 pipeline steels

Abstract

Effects of microstructure on fracture toughness and transition temperature of high-toughness X70 pipeline steels were investigated in this study. Three types of steels were fabricated by varying alloying elements such as C, Cu, and Mo, and their microstructures were varied by rolling conditions such as finish rolling temperature and finish cooling temperature. Charpy V-notch (CVN) impact tests and pressed notch drop-weight tear tests (DWTT) were conducted on the rolled steel specimens. The Charpy impact test results indicated that the specimens rolled in the single-phase region of the steel containing a reduced amount of C and Mo had the highest upper shelf energy (USE) and the lowest energy transition temperature (ETT) because of the appropriate formation of acicular, quasipolygonal, or polygonal ferrite and the decreased fraction of martensite-austenite constituents. Most of the specimens rolled in the single-phase region also showed excellent DWTT properties as the percent shear area (pct SA) well exceeded 85 pct, irrespective of finish cooling temperatures, while their USE was higher than that of the specimens rolled in the two-phase region. Thus, overall fracture properties of the specimens rolled in the single-phase region were better than those of the specimens rolled in the two-phase region, considering both USE and pct SA.

Effect of Nd3+ Ion Concentration on the Corrosion Resistance of API X70 Steel in Chloride‐Rich Environments

“…It is known that depending on the manufacturing conditions and thermal treatments to which an X70 steel is subjected, its microstructure can be formed by the presence of different phases, the main being the polygonal ferrite, quasipolygonal ferrite, Widmanstätten ferrite, acicular ferrite, bainitic granular ferrite, bainite ferrite, martensite in addition to the presence of precipitates (Nb(CN), Fe 3 C, MnS, and SiO 2 ) [33][34][35]. is combination of phases can favor a galvanic effect between them, causing the corrosion of the electrochemically less stable phase, generally the ferrite [36], in addition to a nonuniform distribution of the local anodic/cathodic ratio that favors localized corrosion [37].…”

Microstructure Evolution of Grade X100 Pipeline under Plastic Deformation Condition

“…A large number of high density dislocation tangle distributed in the ferrite plank internal, which improved remarkably tensiles strength of the grade X100 pipeline. This kind of tangled or the existence node's dislocated grid configuration is advantageous to the dislocation stabilization and maintains high dislocation density [12][13][14][15]. The ferrite plank (length) the axial ratio approximately is 3 : 1.…”

On the Post-Printing Heat Treatment of a Wire Arc Additively Manufactured ER70S Part

“…It is well established that the presence of acicular ferrite and bainite constituents in the microstructure of steels can promote the mechanical properties of the component. This is primarily resulted from the finer structure of both phases, a more uniform distribution of carbide and higher dislocation density and internal stresses in the bainite phase, contributing to a higher hardness/strength and ductility in the alloy [26][27][28]. However, it should be noted that since the volume fraction of acicular ferrite and bainite constituents are negligible as compared to the dominant ferritic and pearlitic microstructure of the alloy, the presence of acicular ferrite and bainite cannot have a significant contribution to the mechanical properties of the WAAM-ER70S sample.…”